SOLVED: zypper: Cannot write file '/var/adm/mount/AP...'

Immediately after installing Leap 42.1 on my hp laptop, “zypper up” complained with

Refreshing <repo names>
...
Cannot write file '/var/adm/mount/AP_hdgfyx'
Abort/Retry/Ignore?

Of course, this directory was okay and writable, root partition was not filled up, cleaning up by rm /var/adm/mount/* didn’t help, either…

To cut a long story short: I could get rid of that error by cleaning up all repositories’ metadata and refreshing it by running

# zypper cc -a
# zypper refresh

After that, “zypper up” went well.

As I couldn’t find any occurence of this problem anwhere else, I thought it worth to be mentioned (and to be searchable) here.
Hope this helps anyone out there.